How does the stock AC center vent mount?

[jcfoote60]

I was looking through the boxes for my Vintage air setup and started test fitting some stuff. I had welded in an AC dash (bare) and now that I'm fitting things up from Vintage I noticed the chrome center vent I got from them mounts with studs to the provided plenum. However where the stock AC vent hole is in my dash, I have 4 small screw holes at each corner? Was there some kind of additional plate that screwed into the dash, then the vent into the plenum???

Does anyone have pictures of how a stock AC vent mounts or have info? Thanks!!

JC